Many techniques have been devised with respect to an apparatus which displays a video by projection. For example, an operation detection apparatus which “detects operation information without using special equipment” and a program thereof are described as a purpose in Patent Document 1.
Further, as means for achieving the purpose, Patent Document 1 discloses “an operation detection apparatus used together with illumination means and image capture means, the apparatus including: means for causing the image capture means to capture an operator with the operator illuminated by the illumination means; means for detecting a region of a specific part of the operator based on image data of the operator obtained by the image capture means; means for extracting a portion of a shadow from the detected region of the specific part of the operator; and means for detecting a plurality of segments each having an edge forming a straight line from the extracted portion of the shadow, detecting a point where the detected segments intersect one another at an acute angle, and detecting the point of intersection as a finger pointing position within the region of the specific part of the operator”.